The present invention is an improvement on structures of the type shown in U.S. Pat. No. 3,517,782 to E. J. Hayes, and U.S. Pat. No. 3,789,961 to Warwick dated Feb. 5, 1974.
For sometime now, automative vehicles have been provided with a dual hydraulic 2+ 2 braking system. In such system there is provided a master cylinder having two fluid pressurizing chambers operable from a single foot pedal. Each of the fluid pressurizing chambers supplies hydraulic brake fluid under pressure to separate hydraulic sub-systems. Currently, one of the sub-systems has communicated with the wheel cylinders of the two front wheel brakes, and the second of the hydraulic fluid sub-systems has communicated with the two wheel cylinders of the rear wheel brakes. Thus, if one of the hydraulic sub-systems does fail, the vehicle would still have an intact hydraulic sub-system for operating the remaining front or rear brakes only.
It has been found that the major portion of the braking of an automotive vehicle is accomplished by the front wheel brakes. Thus, from 60% to 70% of the braking effort is handled by the front wheel brakes, and the balance by the rear brakes.
To accommodate this difference due to an apparent weight shift forward in the act of braking a car, the industry has resorted to wheel cylinders which can be actuated from either of the two hydraulic sub-systems. The disc brake caliper assembly as described in the aforesaid patents are of this type.
In the manufacture of such devices, a caliper casting is formed having first and second legs joined by a transverse member which when installed spans the disc rotor and disposes the legs on opposite sides of said rotor. The first or inward leg is fabricated to contain the piston assembly which moves a disc brake pad against the inner surface of the disc rotor, and simultaneously moves the entire caliper housing inwardly relative to the disc rotor forcing the second or outer leg of the caliper to carry its associated disc pad also into engagement with the outer surface of the disc rotor. This is the floating caliper type of disc brake.
As will be readily seen from each of these patents, the bore for the cup-shaped piston member in the first leg must be made by passing the boring tool through an accommodating opening in the second or outer leg. This bore has an annular shape rather than a cylindrical shape. The attempt to maintain tolerances with a tool spaced so far from its chucking means is often thwarted. The present invention obviates this difficulty.
Also, as will be seen from each of the foregoing patents, there is provided a dust boot to prevent introduction of foreign matter between the relatively moving metal surfaces of the cup-shaped piston and its annular cylinder walls. The normal assembly procedure is to insert the dust boot into the caliper body and engage it therewith, and then insert the cup-shaped piston through the necked-down inner ring of the dust boot. This procedure, of course, involves stretching the necked-down portion of the dust boot while a considerable length of the cup-shaped piston is being passed therethrough.
According to the present structure, the problem of affixing the dust boot is facilitated.